742 ANNUAL REPORT SMITHSONIAN INSTITUTION, 192 8 



racy of thermochemical measurements. This was largely effected by 

 means of the " adiabatic calorimeter," in which the calorimeter is 

 surrounded with a larger vessel the temperature of which is caused 

 to follow closely that of the calorimeter during the experiment. 

 This ingenious device, original with Richards, although the sugges- 

 tion had been made earlier by Person, enables the troublesome cor- 

 rections for loss of heat to or gain of heat from the surroundings, 

 and for lag of the thermometer, to be avoided. With this apparatus 

 he made accurate measurements of the specific heats of solids at low 

 temperatures, the specific heats of liquids, the heats of evaporation of 

 liquids, the heats of solution of metals in acids, the heats of combus- 

 tion of organic substances, and heats of neutralization. 



From a theoretical point of view he early recognized the im- 

 portance of alteration in the heat capacity of a system undergoing a 

 chemical change, and several years before the publication of the 

 third law of thermodynamics by Nernst he pointed out the close re- 

 lation between this alteration and the difference between the " total 

 energy change " and the " free energ}^ change " during a chemical 

 reaction, together with the high probability that this difference grad- 

 ually disappears as the absolute zero of temperature is approached. 



Richards was the first to make exact determinations of the transi- 

 tion temperatures of hydrated salts, and to suggest their advantages 

 as fixed points in thermometry, since extreme alterations in the tem- 

 perature of the thermometer may be avoided by their use. 



In electrochemistry Richards made very detailed investigations of 

 the copper and silver coulometers and showed that Faraday's law 

 holds with great exactness both in aqueous solution and with fused 

 salts. The study of single potential differences, especially that of 

 iron under varying conditions, and of the electromotive forces be- 

 tween amalgams of different concentrations with their theoretical 

 implications engaged his attention at various times. 



For more than 25 years Richards's activity was very largely con- 

 cerned with the experimental and theoretical consideration of the 

 apparent volumes and compressibilities of the chemical elements. 

 Experimentally this involved the devising and using of new forms 

 of apparatus for the very exact measurement of the compressibilities 

 of the elements and their compounds, as well as the related proper- 

 ties, surface tension, and heat of evaporation. He first developed 

 clearly the close parallelism and periodicity of atomic volume and 

 compressibility, and the relations between compressibility and in- 

 crease or decrease in volume during a chemical change on the one 

 hand and chemical affinity and cohesion on the other, and called 

 attention to the extreme improbability of constant atomic volume of 

 an element in different states of chemical combination. In this work 

 he was led to very definite and interesting ideas as to the effect of 



